The present invention generally relates to jitter compensation systems in rotary recording medium reproducing apparatuses, and more particularly to a jitter compensation system which uses a phase locked loop to drive a jitter compensation mechanism for a reproducing element of a reproducing transducer by an output of the phase locked loop, and compensate the jitter of a carrier chrominance signal of a reproduced color video signal in a reproducing circuit.
Reproducing apparatuses have been reduced to practical use, in which a recorded signal in a rotary recording medium (hereinafter simply referred to as a disc) in which an information signal such as a video signal and an audio signal is recorded as a variation in geometrical configuration, is reproduced as a variation in electrostatic capacitance between an electrode of a reproducing stylus of the reproducing transducer and the recording surface of the disc. However, when irregularity (wow and flutter) exists in the rotation of the turntable on which the disc is placed to rotate therewith, eccentricity exists in the center hole of the disc, distortion is introduced in the disc upon molding of the disc, and the like, jitter (error in the time axis) is introduced in the reproduced signal. The above jitter covers a frequency range form a relatively low frequency component corresponding to the rotational period of the disc due to such causes as the above irregular rotation and eccentric center hole, to a relatively high frequency component due to such causes as the above distortion in the disc, mainly, few hundreds Hz to 1.5 kHz.
In a case where the reproduced information signal is a color video signal, the above jitter gives rise to color shading, swinging of picture image in the reproduced picture of the receiver, and the quality of the reproduced picture greatly deteriorates.
Accordingly, in a conventional system (e.g. U.S. Pat. No. 3,967,311 granted to Fuhrer on June 29, 1976), a chrominance subcarrier of the reproduced color video signal, which has been frequency converted into a low frequency range, is frequency-converted (hererodyne-converted) back to the original chrominance subcarrier frequency, and the phases of this chrominance subcarrier which is frequency-converted into the original chrominance subcarrier frequency, and a reference signal are compared. An output error signal obtained as a result of the above phase comparison controls an oscillator which generates a signal for performing the above frequency conversion, to reduce the error in the time axis upon frequency conversion. Furthermore, the cantilever which is provided with the reproducing stylus at the tip end thereof, is displaced towards a relative scanning direction of the reproducing stylus with respect to the disc, by the above output error signal. Hence, in the above conventional system, jitter compensation was performed by performing the above control operation in order to prevent the introduction of error in the time axis.
However, in the above conventional system, the output error signal obtained as a result of the phase comparison is established so as to have a characteristic suited for controlling the oscillator which generates the signal for performing the above frequency conversion. Therefore, the above output error signal is not necessarily suited for driving a jitter compensation mechanism (so-called arm stretcher) which displaces the above cantilever. Moreover, there was a disadvantage in that even when phase compensation is performed on the above ouput error signal, the jitter compensation cannot be sufficiently performed.
In addition, as another conventional system, (e.g. as described in column 1, lines 54 to 62 of U.S. Pat. No. 3,967,311, granted to Fuhrer on June 29, 1976); and there was a jitter compensation system provided with a first circuit system which compares the phases of the horizontal synchronizing signal obtained from the reproduced color video signal and the output signal of a crystal oscillator, to drive the jitter compensation mechanism for the reproducing transducer by the output error signal, obtained as a result of the phase comparison. Another system was tested that has a second circuit system which compares the phases of the carrier chrominance signal, which has been converted into a low frequency range, separated from the reproduced color video signal and the output signal of a crystal oscillator, to control the oscillation frequency of a voltage controlled oscillator which produces a signal for frequency-converting the frequency of the carrier chrominance signal, which has been converted into the low frequency range and back to the original frequency.
However, in the tested system, the above first and second circuit systems are constructed to operate independently without having a mutual relationship with each other. Accordingly, the circuit system became large as a whole, and the construction of the system became complex. Hence, there were disadvantages in that the circuit system could not be simplified, and the system could not be manufactured at low cost.